1. Field of the Invention
The present invention relates to an optical fiber preform and to a method of manufacturing an optical fiber using the optical fiber preform.
2. Description of the Related Art
One method of manufacturing an optical fiber is known as an Online-Rod in Cylinder method. In this method, a core rod that either forms a core or forms a core and a portion of the cladding is inserted inside an internal space in a quartz tube that forms a cladding. When this is drawn into a fiber, at the same time as the fiber drawing is taking place, the quartz tube and the core rod are fused together into a single body so as to manufacture a bare optical fiber. A coating layer is then provided on the bare optical fiber so as to form an optical fiber.
In this Online-Rod in Cylinder method, the shape of the distal end portion of the optical fiber preform that is formed by the quartz tube and the core rod which is inserted inside the quartz tube is crucial from the standpoints of the workability of the fiber-drawing operation, manufacturability, the property stabilization of the optical fiber, cost, and the like.
In Japanese Unexamined Patent Application, First Publication No. 2004-43201, a method for manufacturing the optical fiber preform that is used in this Online-Rod in Cylinder method is disclosed in which heat is applied to the distal end portion of the quartz tube so as to seal it off in a tapered shape, and heat is also applied in the same way to the distal end portion of the core rod so as to also form the portion in a tapered shape. Next, the core rod is inserted inside the quartz tube so as to form an optical fiber preform.
In Japanese Unexamined Patent Application, First Publication No. 2006-27924, a method is disclosed in which, after the core rod has been inserted inside the quartz tube, heat is applied to the distal end portion thereof so as to form a distal end tapered portion, and thereby form an optical fiber preform.
However, in these conventional technologies, because either the quartz tube and the core rod are heated separately, or else the joint object formed by combining the quartz tube and the core rod is heated, a component having a large thermal capacity must be heated, so that the time required for this heating is prolonged to several hours or more.
In recent times, the size of the optical fiber preform is increasing, so that the sizes of the quartz tube and core rod are also increasing, and thus, the heating time requires much longer time.